Trust pervades human societies1,2. Trust is indispensable in friendship, love, families and in organizations. In addition, it plays a key role in economic exchange and politics3. In the absence of trust among trading partners, market transactions break down. In the absence of trust in a country?s institutions and leaders, political legitimacy breaks down. Much recent evidence indicates that trust contributes to economic, political and social success4-6. Little is known, however, about the biological basis of trust among humans. Here we show that the intranasal administration of oxytocin, a neuropeptide that plays a key role in social attachment and affiliation in non-human mammals7-9, causes a substantial increase in human trust, thereby greatly increasing the social benefits from human interactions. Moreover, this increase in trust seems entirely based on the affective, and not on the calculative, components of trust because subjects who receive oxytocin do not have more optimistic expectations about the trustworthiness of their interaction partners. Interestingly, although oxytocin increases trust, it does not affect human trustworthiness. These data concur with animal research suggesting an essential role of oxytocin as a biological basis of prosocial approach behaviour.

This paper introduces an emerging transdisciplinary field known as neuroeconomics. Neuroeconomics uses neuroscientific measurement techniques to investigate how decisions are made. First, I present a basic overview of neuroanatomy and explain how brain activity is measured. Then I survey findings from the neuroeconomics literature on acquiring rewards and avoiding losses, learning, choice under risk and ambiguity, delay of gratification, the role of emotions in decision-making, strategic decisions, and social decisions. I conclude by identifying new directions that neuroeconomics is taking, including applications to public policy and law.

Human beings exhibit substantial interpersonal trust ? even with strangers. The neuroactive hormone oxytocin facilitates social recognition in animals, and we examine if oxytocin is related to trustworthiness between humans. This paper reports the results of an experiment to test this hypothesis, where trust and trustworthiness are measured using the sequential anonymous ?trust game? with monetary payoffs. We find that oxytocin levels are higher in subjects who receive a monetary transfer that reflects an intention of trust relative to an unintentional monetary transfer of the same amount. In addition, higher oxytocin levels are associated with trustworthy behavior (the reciprocation of trust). Absent intentionality, both the oxytocin and behavioral responses are extinguished. We also find that ovulating females are less trustworthy, consistent with the inhibition of oxytocin binding by progesterone. We conclude that perceptions of intentions of trust affect levels of circulating oxytocin.